Method of casting lead-bearing steel



Patented Aug. 26, 1941 METHOD OF CASTING LEAD-BEARING STEEL Wilbur A.Saylor, Bellevue, Pa., and Laurin D. Woodworth, Youngstown, Ohio NoDrawing.

Application July20, 1939,

Serial No. 285,628

1 Claim.

The present invention relates to the preparation of steel ingot moldsused in the casting of steel ingots to which lead or lead alloys are tbe added.

It is a recognized fact that lead added to steel, in a manner to obtainthorough mixing and distribution of the lead in the steel, is beneficialin that it develops exceptionally good machining properties inthe steelso treated. Ihe addition of lead differs from elements generally addedto steel in that it neither combines nor alloys with iron, so that itsbeneficial efiects depend upon diffusing or distributing the lead in thesteel. To effect this diffusion of the lead, it is added in the form offine shot to the steel as it is being teemed into the mold, because thelead, having a density nearly one and one-half times that of moltensteel, tends to sink rapidly to the bottom of the mold or ladle of steelto which it is added if it is added in the form of larger pieces. Thelead shot used is preferably .02 inch in diameter, although it may beused in slightly larger or smaller particles.

In the usual practice of casting ingots of ordinary grades of steel, themetal is teemed through an opening in the bottom of the ladle, thestream of molten metal entering the top of the mold as near the centerline of the latter as possible. When lead additions are to be made tosuch steels, the lead in the form of fine shot is added through a small,inclined trough or chute so that the stream of lead shot descendsadjacent to or with the stream of metal.

Since lead has a boiling point slightly lower than the temperature ofthe liquid steel, a certain amount is lost through volatilization. Whenlead is added to steel cast in the usual cast iron molds, a certainproportion of the lead added is lost in other ways also. When the ingotsare stripped, a portion of the lead that has been added is found on theoutside walls of the ingot and upon the stool at the bottom of theingot, the stool being a flat base upon which the ingot is cast and uponwhich it stands after solidification. These observations have provedthat part' of the lead added is deposited at the outer surface of theingot or between the ingot moldand the steel. Also, some of the lead isdeflected as it is dropped into the mold and when it strikes the baremold wall, it 'has a tendency to adhere or freeze to the mold, sincefthelatter is at a temperature somewhat below the melting point of the lead.The lead particles as they strike the mold appear to be in a moltenconditionand are certainly at a temperature near their melting 55 point,which is sufficient to render the lead very soft and almost fluid-like.In either condition, the particles of lead are not deflected by the coldmold wall, but adhere to it. Also, the turbulence at the surface of themolten steel in the mold, produced by the flow of the stream from theladle, tends to deflect some of the lead towards the mold wall as itstrikes the surface of the molten steel. The lead thus deflected towardsthe mold melts as the steel rises above it, and when the lattercontracts ,and cools to form a gap between it and the mold, the leadupon the mold, as well as part of that mingled with the steel at thesurface, melts and tends to flow downward between the mold and the ingotsurface.

It will thus be apparent that the lead concentrated at the surface ofthe ingot has the effect of producing a deleterious surface condition onthe ingot. When the ingot is stripped, that is, when the mold isremoved, the lead appears to adhere to the ingot where some of it isvolatilized, hence contaminating the air with lead fumes. Some is alsooxidized by the oxygen of the air, forming a finely divided lead oxidepowder which tends to further contaminate the air, while the lead whichdoes not escape into the air trickles down over the surface of the hotingot. The lead volatilized or oxidized contaminates the air increasingthe hazard to the workmen in the vicinity.

Under the present invention, the aforementioned defects are eliminatedand it is possible to prevent the accumulation of lead on the surface ofsteel ingots to which lead is added without changing the usual practicein adding the lead.

An object of the present invention is to prevent the accumulation oflead on the surfaces of the ingot and reduce the amount volatilized bycoating the interior of the mold with a viscous, semi-fluid,carbonaceous mixture.

Another object of the present invention is to obtain a greaterproportion and a more uniform I distribution of lead from the top to thebottom of the ingot.

A further object is to treat the mold interior so as to produce ingotshaving clean sides and free from flaky lead-iron oxide compounds andthereby reduce contamination of the atmosphere by the lead fumes anddust.

Other objects and advantages will become apparent as the descriptionproceeds.

As a specific example only, of the method of the present invention,there is subsequently described in detail the procedure of applying coaltar to the interior of the mold.

The coal tar preferred for use is .the virgin product obtained in thecoking of coal to metallurgical coke by the by-product process, which isthe process now almost universally employed for the production of cokefor the blast furnaces. Under some conditions of production and handlingthis tar contains pitch-like bodies, which, if present, are removed byheating and straining the tar through a screen .or sieve. Whether these:bodies are present or not, the tar is maintained at a temperaturebetween 90 degrees and 140 degrees Fahrenheit to render it sufficientlyfluid to facilitate the next operation, which consists of applying it tothe interior of the mold.

In the use of virgin tar, it has been found necessary to control thetemperature of the molds, so that the heat of the mold will distill someof the more volatile constituents of the tar, leaving a somewhat gummyresidue that will adhere firmly to the mold and not be rendered toofluid from the heat of the stream of liquid steel during the teeming.The most desirable temperature of the molds for application of the taris between 150 degrees and 300 degrees Fahrenheit. In regular operation,this temperature range can be obtained by permitting the molds to cooland applying the tar promptly when they have cooled to within thistemperature range.

The most desirable manner of coating the interior of the molds is toapply the tar by spraying. For this operation, a number of known devicesare available for use, the chief requirement being that the fluid tar beintroduced into the spray nozzle or nozzles under suificient head vices,the tar may be applied to the mold while, it is in any position, but itis usually most conveniently applied with the mold in an uprightposition. After applying the tar, the mold should be permitted to standuntil it has cooled somewhat before .it is used for making a leadedsteel ingot.

The tar may .be applied, if desired, with long handled brushes, butifapplied in this manner, it is desirable to have the temperature of thetar and of the molds on the low side of the ranges, hereinabovementioned, and the molds supported in an inclined position. Also, themolds should stand for a longer time before they are used for castingingots.

Other fluid or semi-fluid mixtures of carbonaceous materials, such asasphaltum pitches andpetroleum residues may besuccessfully employed andapplied in the manner similar to that described for tar. In the use ofany of these mixtures, a requirement is that they be applied underconditions that will give a soft paste-like coating at the higher moldtemperatures mentioned above and will not be converted into a coke-likemass containing little or no volatile matter when the steel is teemedinto the mold.

As steel is teemed into a mold having its interior coated as hereinabovedescribed, certain effects produced at the border line described by theliquid steel in contact with the mold are most helpful in accomplishingthe desired result. Thus, as the liquid steel surface rises in the mold,the heat therefrom causes a rapid distillation of the volatileconstituents of the coating which fills the mold with a reducingatmosphere so that the lead is not oxidized and any particles of thismetal that may be adhering to the coating are projected back into theliquid steel. Also, the absorption of carbon :by the steel along thisline causes an evolution of gas and a certain agitation of the metalwhich prevents any small particles of lead momentarily in motion on thesurface of the liquid steel from coming into contact with the relativelycold mold.

The results obtained by the present invention may be by variousmodifications in the coating mixtures used, the methods of applying thecoatings to the molds, and the method of introducing and mixing the twometals in the mold. For example, the steel may be bottom-poured; thatis, the liquid steel may be introduced through a runner entering themold at the bottom, while the lead is scattered upon the rising surfaceof liquid steel in the mold.

While we have described a specific embodiment of the present invention,it will be seen that we do not wish to be limited exactly thereto, sincevarious modifications may be made without departing from the scope ofthe invention, as defined by the following claim.

We claim:

The method of manufacturing lead-bearing steel which consists inpreparing the ingot molds by applying a coating of virgin tar to theirinner surfaces while said molds are at a temperature of from about 150F. to 300 F., permitting the molds to stand to expel those constituentsof the coating volatilizable at said mold temperature, teeming moltensteel into the molds and simultaneously adding lead thereto, saidcoating increasing the proportion of lead retained in the

